a) Sun and daylight

Starting from a Reference south oriented facade equipped with solar control windows, two examples of substitution with glass collector were simulated to evaluate the incidence on the building’s luminosity figure 4, Variation 1 and Variation 2.

Variation 1 : The comparison with the Reference case permits to notice that the integration of the glass collector in lower side of the facade reduces notably the over-heating in the summer and middle seasons. It contributes to the sun and daylight distribution. In middle seasons and in winter its effects improve the light on the far end of the buildings. In all seasons its influence on daylight is negligible. The glass collector in the lower side of the facade does not introduce more electric lighting.

Variation 2 : The comparison with the Reference case permits to notice that the vertical integration and in the lower side of facade increase the limitation of over-heating in summer and middle seasons. In middle seasons and in winter its effects tend to be the same at the far end of the building than in the Reference case.

In all seasons its influence on daylight is minimal. The integration in vertical position and in the lower side of the facade introduces small electric lighting loads in summer.

The influence of its vertical position is not neutral and takes advantage of raytracing simulation.

The results given hereafter are extrapolated from Fraunhofer-ISE measurements, to take into account the evolution of the geometry of the glass collector between the current and the tested version [2].

Optical transmission:

The evolution of the optical transmission coefficient (t) function of incidence angle is given by figure 6.

The comparison of the curves relating to the transmission coefficient of an insulated glass with solar control, clearly shows the effect of the reflectors on the direct transmission of solar flow.

This effect is of course under-evaluated, if we take into account the thermal re-emission, due to the exchange between inside glass position 4 and inner building by convection and infra-red radiation.

Solar factor

The net solar flow in the room is the sum of three components :

• a first component is the optical transmission, figure 1,

• a second component is the thermal re-emission,

• a third component is the exchange between the solar collector and inner building. This last component represents the losses of the solar collector, in position 4. The relation which expresses the net flow is:

Qnet = x• IT • S + hi • a2 • S-(0v -0,)+ Umt • a, • S-(0c -0,) (5)

The experimental values established by Fraunhofer ISE [2] were obtained in accordance with calorimetric measurements in complex glazing [4], by considering the same temperatures for the interior, for the exterior and for the absorber. Thus the g solar factor does not take into account the 3rd component. The evolution of g according to the angle of incidence is given in the figure 6.

If we integrate the losses of the solar collector to the interior, we obtain a new estimation of an equivalent g-value. A very unfavorable assumption of its evolution curve is given in figure 6, with an absorber temperature of 80°C.

In this case, we notice that the net solar flow, Qnet accounts for approximately 20% of incident solar flow. This value is to be compared with a 0.33 g-value of a double glazing with solar control.